The PAC heard evidence Mr Kirby failed to act on DfT orders that the redundancy scheme should be restricted to statutory levels.

In a hard-hitting report it stated that the payments proceeded because of "weak internal processes at HS2 Ltd" which stopped decision-making and scrutiny bodies from receiving accurate information.

The relationship between the DfT and the company "was not robust enough to prevent this", the committee added.

It called on both organisations to "carefully consider whether any further action can now be taken" against Mr Kirby, who left his role as chief executive in December 2016 and is now chief operating officer at aerospace giant Rolls-Royce.

He has previously denied "any allegation of wrongdoing".

Labour's shadow transport secretary Andy McDonald accused Transport Secretary Chris Grayling of having a "cavalier attitude towards the nation's finances" and called on him to "take responsibility and spell out what he will do to prevent any more public money being squandered".

Transport and Salaried Staffs Association leader Manuel Cortes described the PAC report as "damning beyond belief" and claimed "heads really must roll at the Department for Transport".

He said: "Simon Kirby did the honourable thing and jumped to avoid being pushed.

"But it is Transport Secretary Chris Grayling who must shoulder the blame for the mismanagement of a vital public infrastructure project by his department that has led to these millions being siphoned out of the public purse."

A National Audit Office report into HS2 Ltd's 2016/17 accounts found it made payments totalling £1.76 million which were not appropriately authorised.

The company agreed compensation worth one month's salary per year of service with outgoing staff to coincide with its headquarters moving from London to Birmingham.

The statutory standard is roughly one week's pay per year depending on age and length of employment.

Some staff were even offered paid leave to top up their exit packages above the £95,000 civil service compensation scheme limit.